The Extensor Hallucis Brevis is a muscle of the foot that primarily assists in extending the big toe. Though it is small in size, its function is crucial in facilitating the fine motor movements and balance of the foot.
Where is Extensor hallucis brevis Located?
The Extensor Hallucis Brevis is located on the dorsal (top) side of the foot, situated medially and is one of the muscles responsible for the dorsiflexion of the toes.
Origin and Insertion
Origin: It originates from the calcaneus, specifically the dorsal surface of the calcaneocuboid joint and the ligaments connecting the base of the fifth metatarsal to the cuboid bone.
Insertion: The muscle transitions into a tendon as it courses distally and inserts onto the base of the proximal phalanx of the big toe.
Structure & Appearance
The Extensor Hallucis Brevis is a thin muscle lying alongside its larger neighbor, the Extensor Digitorum Brevis. Together, these muscles form a broad expansion on the dorsum of the foot, distinguishing themselves from the larger extensor tendons of the leg.
Functions
- Toe Extension: Its primary function is to extend the big toe. By doing this, it aids in balancing the foot when walking, especially during push-off.
- Foot Stability: The EHB, along with other extensor muscles, plays a role in stabilizing the foot, especially when bearing weight.
- Assisting in Dorsiflexion: While the main dorsiflexion of the foot is achieved by muscles in the anterior compartment of the leg, the EHB aids in this motion, especially during movements that require precision.
Innervation: The Extensor Hallucis Brevis is innervated by the deep fibular (peroneal) nerve.
Blood Supply: Its blood supply is mainly derived from the dorsalis pedis artery, ensuring that the muscle gets an adequate supply of nutrients and oxygen.
Clinical Significance
- Entrapment Neuropathy: The deep fibular (peroneal) nerve, which innervates the EHB, can become compressed or entrapped as it courses through the foot, leading to pain, tingling, or muscle weakness. This condition might specifically affect the function of the EHB.
- Hallux Valgus (Bunions): Though the primary factors causing bunions are structural and genetic, weakness or dysfunction in the EHB might exacerbate the deviation of the big toe. Proper functioning of the EHB can provide some degree of resistance to the lateral deviation of the big toe in hallux valgus.
- Trauma and Tears: Like all muscles, the EHB can suffer strains or tears, especially in individuals who participate in activities requiring repetitive toe extension or sudden forceful movements, such as ballet dancers or athletes. Such injuries may present as pain on the dorsum of the foot, especially during toe extension.
- Surgical Recognition: When performing surgeries on the dorsum of the foot, recognizing and preserving the EHB is important. Its proximity to the extensor digitorum brevis means that surgical interventions in that area should be undertaken with care to prevent unintended damage to the EHB.
- Gait Analysis: Weakness or dysfunction of the EHB can be a component of a more comprehensive gait abnormality. It may impact the toe-off phase of walking, potentially leading to compensatory movements elsewhere in the foot or leg.
